1. Field of the Invention
This invention relates to the heat treating of glass sheets, particularly the heat treating of flat glass sheets while the latter are conveyed in a horizontal orientation along a horizontally extending path through a heating furnace, where glass sheets are heated to an elevated temperature sufficient for further fabricating processes, such as tempering, annealing and coating by the application of coating compositions which, on contacting a heated glass surface, form a coating that bonds strongly thereto.
In the heat treating of glass sheets, particularly flat glass sheets, a succession of glass sheets is conveyed through a tunnel-type of furnace comprising a plurality of spaced, horizontally extending rolls, each extending transversely of the furnace to provide a horizontally extending path through the furnace. In the past, glass sheets were likely to become scuffed or provided with a defect known as roll ripple distortion as the glass sheets were engaged completely across their dimensions extending transverse to the direction of movement by rolls extending continuously across the extent of the furnace. Any misaligned rolls at a higher elevation than other rolls tended to mark and distort the glass. Furthermore, since different portions of the heating furnace are at different temperatures, the rolls at different portions of the furnace tended to increase in length to a different degree in different portions of the furnace, thereby developing a different amount of sag. Prior to the present invention, attempts were made to counteract this sag by imparting stress to the rolls that tended to bow them upward in their glass engaging regions. Thus, such glass sheets were engaged in their central portions of the vision area so that any variation from roll to roll would have a harmful effect on the optical properties of glass sheets so treated.
Another effect prominent in glass sheet conveying rolls when rotating at high speed is the tendency of the rolls to whip. This whipping tends to raise and lower different portions of a glass sheet as the latter is conveyed over each different roll. This defects resulting from this whipping of the rolls is further complicated by the fact that different conveyor rolls do not whip in unison with one another so that such non-uniform whipping further complicates the resulting defect pattern.
2. Description of the Prior Art
U.S. Pat. Nos. 1,879,998 and 1,885,306 to Sylvester disclose bearing arrangements for rotatably supporting glass sheet conveyer rolls which may be adjusted vertically to deflect the body portions of the roll to a slight degree to develop a convex shape in elevation or "crown" that counteracts the tendency of the roll to sag under heat and weight.
Other pertinent patents discovered in a novelty search include U.S. Pat. Nos. 886,998 to Love; 1,856,668 to Sylvester; 1,851,609 to Waldron; 1,868,060 and 1,889,082 to Von Reis; 2,135,175 to Fallon; 2,676,387 to McArn; 3,086,279 to Alexeff; 3,424,651 to DeNoyer et al and 3,881,906 to Ritter et al. In addition, British patent specification No. 1,035,527 to Justus was also reported in a novelty search.
The gist of the various patents relates to apparatus for mounting a roll that is subject to a load tending to effect downward deflection or sag in the center portion of the roll axis and means for counterbalancing such sag.